In the fields of deodorization, exhaust gas treatment, and the like, various adsorbent materials have so far been developed. Activated carbon is a representative example of these, and it has been used widely in various industries for the purpose of air cleaning, desulfurization, denitrification, or removal of harmful substances by making use of its excellent adsorption performance. In recent years, demand for nitrogen has been increasing, for example, in the semiconductor manufacturing process and the like. Such nitrogen is produced from air by using molecular sieving carbon according to the pressure swing adsorption process or temperature swing adsorption process. Molecular sieving carbon is also used for separation and purification of various gases such as purification of hydrogen from a cracked methanol gas.
When a mixture of gases is separated according to the pressure swing adsorption process or temperature swing adsorption process, it is the common practice to separate it based on the difference between the gases in equilibrium adsorption amount or rate of adsorption to molecular sieving carbon or zeolite used as a separation adsorbent material. When the mixture of gases is separated based on the difference in equilibrium adsorption amount, conventional adsorbent materials cannot selectively adsorb thereto only the gas to be removed, and the separation coefficient decreases, making it inevitable that the size of the apparatus used therefor increases. When the mixture of gases is separated into individual gases based on the difference in rate of adsorption, on the other hand, only the gas to be removed can be adsorbed, although it depends on the kind of gas. It is necessary, however, to alternately carry out adsorption and desorption, and also in this case, the apparatus used therefor should be larger.
On the other hand, there has also been developed, as an adsorbent material providing superior adsorption performance, a coordination polymer undergoing a change in dynamic structure when exposed to external stimulation. When this novel coordination polymer undergoing a change in dynamic structure is used as a gas adsorbent material, it does not adsorb a gas until a predetermined pressure but it starts gas adsorption at a pressure exceeding the predetermined pressure. In addition, a phenomenon is observed in which the adsorption starting pressure differs depending on the nature of the gas.
Application of these phenomena to adsorbent materials used in a gas separation apparatus employing a pressure swing adsorption system enables very efficient gas separation. It can also decrease the pressure swing width, contributing to energy savings. Further, it can contribute to size reduction of the gas separation apparatus, making it possible to increase competitiveness in terms of costs when a high-purity gas is put on the market as a product. Moreover, even if the high-purity gas is used in a company's own plant, the costs paid for the equipment requiring a high-purity gas can be reduced, resulting in a reduction of manufacturing costs of the final product.
When a coordination polymer is used as an adsorbent material, it is preferable to use the coordination polymer after molding, rather than in the form of a powder. For example, pelletization by tablet compression is known as a method of molding a coordination polymer (see PTL 1 and PTL 2). However, when the present inventors pelletized, by tablet compression, a coordination polymer undergoing a change in dynamic structure when exposed to external stimulation, it was confirmed that the pellet form could not be maintained after adsorption of gas, because the volume of the coordination polymer undergoing a change in dynamic structure when exposed to external stimulation was expanded upon gas adsorption (see, for example, NPL 1).
Regarding a coordination polymer comprising a copper ion, a tetrafluoroborate ion, and 4,4′-bipyridyl, it is known that the coordination polymer can be formed into pellets by tablet compression when using magnesium stearate as a lubricant, and that the coordination polymer can be formed into granules by using sugar as a binder (see NPL 1). However, the methane adsorption starting pressure of pelletized samples becomes about 1 MPa higher than the starting pressure of powder samples. Thus, the original properties of the coordination polymer cannot be maintained after pelletization.
PTL 3 discloses a heat-conductive resin composition comprising a porous coordination polymer and a thermoplastic resin. As specific examples of the thermoplastic resin, PTL 3 refers to styrene elastomers, polyester elastomers, polyurethane elastomers, and olefin elastomers; however, the obtained composition is not designed for gas adsorption, and nothing of this sort is mentioned in PTL 3.